The objective of this project is to develop a safe, efficacious single dose live attenuated vaccine for prevention of disease in humans caused by dengue virus. A chimeric YF/dengue2 virus (YF/Den2) was constructed using a recombinant cDNA infectious clone of the yellow fever (YF17D) vaccine strain as a backbone into which the premembrane (prM) and envelope (E) genes of a human isolate (PUO218) of dengue-2 virus were inserted. Viruses were recovered upon transfection of Vero cells with mRNA and amplified twice in these cells to yield a titer of 6.3 log(10p)fu/ml. This strategy has been successfully applied for construction of an attenuated chimeric YF-Japanese encephalitis vaccine which is currently in manufacturing. The YF/Den2 virus grows to high titers in acceptable cell lines for human use. In this research project the YF/Den2 chimeric virus will be evaluated in vitro and in vivo. At the completion of this study it will be determined if the chimeric YF/Den2 virus is sufficiently attenuated/immunogenic to be considered as a vaccine candidate for human use. In addition, information obtained from this work will be used to select proper starins (attentuated or wild type) for other 3 dengue serotypes (1,3 and 4) to produce a tetravalent vaccine against all 4 serotypes. PROPOSED COMMERCIAL APPLICATION: Dengue virus is a world-wide public health problem. Over 2 billion persons are at risk of dengue infection and 100 million cases of primary dangue fever and over 450,000 cases of dengue haemorrhagic fever occurs annually. Currently no vaccine available. The vaccine made through this project has a large market potential (> $300 mm/year) and can e used for traveler and military in the US, Europe, Japan, Australia as well as for routine childhood immunization in dengue epidemic/endemic countries.